1. Field of the Invention
The present invention relates to a recording material for the inkjet process, in particular for use with solvent-based pigmented inks.
2. Related Background Art
The inkjet process is now a widely used printing process since it can be carried out using relatively simple printers without noise and with high quality, in particular in the case of color printing. In the inkjet process, droplets of a recording fluid, the ink, are applied to the recording material by various techniques (for example continuous method, drop-on-demand method, such as piezoelectric or bubble jet method). With increasing improvement of the mode of operation of inkjet printers, increasingly high requirements are being set for the recording materials. The recording produced by means of inkjet processes is required to have, for example, high resolution, high color density, sufficient ink gradations and good smear resistance, as well as water resistance and lightfastness.
A recording material for the inkjet process consists as a rule of a substrate and an ink-receptive or recording layer arranged thereon. The recording layer frequently consists of a pigment/binder mixture. In addition to increasing the whiteness of the material, the pigments serve for retention of the colorants from the ink on the surface of the sheet.
European Patent 0 445 327 relates to a recording material having a glossy surface for the inkjet process, comprising a polyolefin-coated base paper and an ink-receptive layer which contains a mixture of gelatine and starch as binder. In one embodiment, the ink-receptive layer additionally contains not more than 5.9% by weight of a porous organic pigment which is a reactive urea/formaldehyde condensate containing methylol groups. The printed images produced have good color density and high abrasion resistance. Although the images are also described as "water-resistant", this "water resistance" is by no means sufficient for the use of the recording material outdoors since the ink-receptive layer itself consists for the most part of water-soluble or water-swellable components. Furthermore, the coating is not highly porous and is suitable only for aqueous inks.
U.S. Pat. No. 4,877,686 describes a recording sheet for inkjet printing which consists of an opaque base sheet and a coating which contains a polyhydroxylic polymer gelled with boric acid or a boric acid derivative, as a binder, and a filler. Inter alia, melamine/formaldehyde pigments are mentioned as possible fillers. Images produced on this recording sheet consist of circular uniform dots.
U.S. Pat. No. 5,081,470 discloses a recording medium for the inkjet process, comprising a substrate and an ink-receptive layer which contains at least 60% by weight of a pigment of a magnesium compound, and a binder. Binders which may be used are water-soluble polymers and water-dispersible polymers alone or in combination. In addition to the magnesium-containing pigments, organic pigments may, inter alia, additionally be present for increasing the ink absorption. The recorded image has good stability, in particular to discoloration, and high optical density.
WO 93/04870 relates to a transparent image-recording element for the inkjet process, which consists of a substrate and an ink-receptive layer, the ink-receptive layer containing a vinylpyrrolidone, disperse polyester particles having a diameter of less than 1 .mu.m, a homopolymer or copolymer of an alkylene oxide, a polyvinyl alcohol, a surfactant and from 0.5 to 1.5% by weight of inert particles having a diameter of 3-25 .mu.m. The inert particles may be organic particles, such as, for example, polymer beads. The ink-receptive layer is capable of controlling the dot size, and the recorded image has improved optical density.
U.S. Pat. No. 4,460,637 discloses an inkjet recording sheet having a support and one or more ink-receptive layers thereon, the ink-receptive layer consisting of a binder and agglomerates of 1-50 .mu.m in average diameter produced by agglomerating primary particles of not more than 0.20 .mu.m in average diameter. The pore radius distribution curve of the pores which are present between the primary particles, i.e. within the agglomerates, has a maximum at 0.05 .mu.m or less. In addition to inorganic pigments, synthetic organic pigments are also mentioned as suitable primary particles. The recorded image is characterized by high ink density and luminous colors and is suitable for multicolor printing.
The abovementioned recording materials are suitable for use with inks which contain soluble dyes. However, for pigmented inks which have, inter alia, the advantage that the images produced therewith are lightfast and hence suitable for outdoor use, no optimal recording materials are known to date. Water-based pigmented inks, solvent-based pigmented inks and wax-based pigmented inks (fusible inks) are known.